1. Field of the Invention
This invention relates to a recording apparatus for effecting recording on a recording medium, and more particularly to a recording apparatus capable of effecting recording of high quality with recording means brought close to a recording medium.
2. Related Background Art
Today, various recording systems have been developed and above all, the ink jet recording system which effects recording by discharging ink droplets in conformity with recording signals has recently been widely used because of the ease with which the compactness and low noise of the apparatus are realized.
In this ink jet recording apparatus, an example of which is shown in FIG. 9 of the accompanying drawings, a recording medium 51 is conveyed to a recording position L by a pair of conveying rollers 50a and 50b and the back of the thus conveyed recording medium 51 is supported by a paper guide 52 and also, an ink jet recording head 53 is driven to discharge ink droplets to the recording medium 51 in conformity with recording signals to thereby accomplish desired recording. After the recording, the recording medium 51 is discharged by a pair of discharge rollers 54a and 54b. In such a recording apparatus, ink droplets discharged from the recording head 53 are very minute and therefore, in order to eliminate the influence of wind or the like to the utmost to thereby obtain a high quality of recording, the distance between the recording head 53 and the paper guide 52 is made small. Design is also made such that the plane to which the paper guide 52 belongs and the point of pressure contact P between the pair of conveying rollers 50a and 50b and the point of pressure contact Q between the pair of discharge rollers 54a and 54b are on the same plane and the recording medium 51 is conveyed rectilinearly.
However, when paper is used as the recording medium 51 and ink is discharged for recording at high density, the paper 51 which has passed the recording area by the recording head 53 is bulged by the permeation of the ink. At this time, there is no escape for the bulged paper and therefore, the paper is expanded toward the recording head 53 side as indicated by the dot-and-dash line in FIG. 9. If this expansion becomes great, the recording head 53 may rub against the recording medium 51 during scanning to thereby stain the recording medium 51 with the recording ink. In an extreme case, the recording head 53 may be caught by the bulged recording medium 51 to thereby cause the jamming of the recording medium. Therefore, distance between the recording head 53 and the paper guide 52 has been limited in being made small.
FIG. 10 of the accompanying drawings shows another example of the prior art.
In FIG. 10, the reference numeral 401 designates a recording head for effecting recording, the reference numeral 402 denotes a carriage carrying the recording head 401 thereon and effecting main scanning in a direction perpendicular to the plane of the drawing sheet, the reference numeral 403 designates a carriage shaft along which the carriage slides, the reference numeral 406 denotes a conveying roller for holding a sheet S and conveying it in the sub-scanning direction, the reference numeral 407 designates a follower roller for urging the sheet S against the conveying roller 406 to thereby create a conveying force, the reference numeral 408 denotes a paper discharging roller for discharging the sheet S, the reference numeral 409 designates a paper discharging follower roller adapted to be urged against the paper discharging roller 408 to thereby create a conveying force, and the reference numeral 410 denotes a recording position at which recording is effected on the sheet S by the recording head 401. The reference numeral 421 designates a supply stacker on which sheets S are stacked, the reference numeral 417 denotes a paper feeding roller for feeding the sheets S on the feeding stacker 421, and the reference numeral 423 designates a discharged paper stacker on which the discharged sheets S are stacked.
The sheets S stacked on the supply stacker 421 are picked up one by one by the paper feeding roller 417 and are fed to the conveying roller 406, and thereafter are conveyed to the recording position 410 by the conveying roller 406. Recording is effected on the sheets S by the recording head 401, whereafter the sheets S are discharged from the recording position 410 by the paper discharging roller 408 and are stacked on the discharged paper stacker 423.
In this example of the prior art, the sheet S is fed to the recording position 410 from the side opposite to the recording head 401, and the discharge direction was parallel to the plane of the recording position or opposite to the recording head 401. In the above-described prior-art recording apparatus, when a rigid sheet such as a postcard is used, the sheet is fed to the recording position 410 from the side opposite to the recording head 401, and this has led to the disadvantage that when the leading end of the sheet is conveyed to the recording position 410 through the point of pressure contact between the conveying roller 406 and the follower roller 407, the leading end of the sheet floats up from the recording position 410 due to the rigidity of the sheet and is liable to contact the recording head 401 when the head effects main scanning, thereby becoming jammed. There has also been the disadvantage that when the sheet is conveyed by only the paper discharging roller 408 after the trailing end of the sheet has passed the point of pressure contact between the conveying roller 406 and the follower roller 407, the trailing end of the sheet likewise floats up from the recording position 410 due to the rigidity of the sheet and is liable to contact the recording head 401 when the head effects main scanning, thereby becoming jammed.
Also, in an ink jet recording apparatus, and particularly a color printer, design has heretofore been made such that as a method of preventing paper floating after recording and imparting tension to a recording surface, paper is pulled by a roller upstream of the recording surface or is adsorbed by air suction or the like. Also, a spur has been provided in a recording medium discharging portion to contrive a countermeasure for paper floating.
The above-described roller construction upstream of discharged paper, however, can only cope with coated paper, and cannot cope with OHP and plain paper which are liable to be print-stained. Also, the construction for air-sucking the recording medium leads not only to the bulkiness of the apparatus, but also to the problem of noise. On the other hand, in an ink jet recording apparatus of the spur construction, there has arisen the problem that by the shape of the projected portion of the spur, ink adhering to the projected portion of the spur stains the white or otherwise colored recording surface of a recording medium such as coated paper, plain paper or OHP. Since the painted surface of coated paper is made of a metallic oxide or a metallic compound of the Si family or Mg family, this projected portion comes to effect paper conveyance at a higher speed, and even if the spur is made of an SUS material, the spur has come to be abraded and slip relative to the recording surface onto which ink has been shot, thereby causing image deterioration. The abraded projection would cause the surface of the paper to be more stained with the ink adhering to the projection.
Also, in the case of a color printer, the influence of the spur in the paper conveying portion differs from that in a monochrome printer, and a slight amount of ink adhering to the spur again becomes wet with the ink on the recording paper shot onto the other color end by the spur being rotated once and thus, color mixing occurs to stain the recording surface. The tip of the projection of the spur becomes rounded from the abrasion of a mold in the punching of a press and the portion thereof which contacts the surface of the paper becomes large, and on OHP, plain paper or the like on which it is difficult for ink to be fixated, the ink is greatly wet with the ink on the surface of the paper and therefore, print stain by the spur is liable to occur. Particularly on OHP, slip occurs between the spur and the surface of unfixated ink liquid on the surface of the paper and a trace like a drawn line is liable to be created by the relative speed. In an ink jet color printer, not only coated paper but also OHP, plain paper or the like is recently used as a recording medium and therefore, when printing is effected on a recording medium of bad fixation, the influence of the abrasion of the projection of the spur by the painted layer of the recording medium occurs more readily and the stain of the printed surface becomes remarkable.
FIGS. 11 and 12 of the accompanying drawings schematically show the stain of the printed surface. FIG. 11 shows the re-melting stain of wet red ink (R) by black ink (Bk). FIG. 12 shows black dots and black lines due to sliding in a case of a sheet 522 of bad fixativeness. Also, FIGS. 13, 14 and 15 of the accompanying drawings show the relation between OHP and the spur, and in these figures the letter C designates a coat layer, and represents the manner in which sliding becomes liable to occur due to the abrasion of a spur projection 509a.